The primary objectives of a replaceable piston in an internal combustion engine are to (1) withstand combustion chamber temperatures and pressures, (2) transmit combustion gas pressure forces to the connecting rod and crankshaft mechanisms without excessive leakage, (3) allow ready access to rings and seals, and (4) be easily replaceable when worn. The replaceable piston should be light weight so that it will not adversely impact maximum performance. It should also be rugged in construction, and low in cost. When the seals, rings or piston are to be replaced, a high degree of reliability is also desirable.
All of the current internal combustion engine pistons known to the applicant require removal from the engine block prior to replacement of rings, seals and disassembly from the connecting rod and crank shaft assembly to replace the piston. If the cylinder is also worn and must be rebored, or a larger bore is desired, or a larger diameter cylinder liner is to be used, a larger diameter piston head must be attached to the connecting rod.
Seal, ring and piston wear is primarily at the piston/cylinder wall interface. Although the piston/connecting rod interface is subject to motion and wear, the non-combustion gas environment and normal availability of lubricants tend to minimize wear at this interface.
Current replaceable liners and piston heads achieve some of the objectives well, but others poorly. Replacement of rings as well as the requirement to remove the piston head from the connecting rod typically requires removal of the entire engine block. New connecting rod attachment must be verified for proper position, lubrication and strength. These actions, handling of other parts, and verifications require added costs and time during replacement primarily of only the piston rings or other piston/cylinder wall interface hardware and parts. Because the entire piston and crankshaft assembly is removed and disconnected, storage and handling tends to be complex and cumbersome, limiting transport, access and use. Also, because of the complete disassembly, new seals, gaskets, pins, etc., are required, possibly adversely impacting reliability.
None of the prior art known to the applicant limits replacement hardware to the worn seals, rings or interfaces or avoids the need to remove the piston head from the connecting rod.
What is needed is a piston head which does not required extraneous disassembly to replace worn rings, seals or portions of the piston. The need for quick and convenient replacement is especially desired in a racing car environment or 2 cycle engine applications, where frequent replacements are common; and must sometimes be performed quickly in the pit in the course of a race.